In recent years, as a filter for removing fine particles such as ions from water, another solution, or gas, a filter molded article employing a graphene having fine water passage holes formed has come to be used (Patent Literature 1).
In general, a graphene is formed on a surface of a copper foil or the like by a chemical vapor deposition (CVD) method (Patent Literature 2). Therefore, conventionally, a step of transferring the graphene to a desired support, called transfer, has been necessary when the graphene is used as a filter molded article (Patent Literature 3).
In the transfer step, an exposed surface of the graphene formed on a copper foil is spin-coated with PMMA to form and dry a thin protective film. Thereafter, the resulting product is floated in a Cu etching solution heated to 50° C. with the copper foil facing downward to remove the copper foil.
Subsequently, the thin film formed of PMMA and the graphene is washed with ultrapure water, and is scooped up so as to be placed on a silicon substrate having a hydrophilized surface.
Thereafter, the above thin film is scooped up with a desired support formed of a resin or the like, and is dried. Immersion in acetone and immersion in IPA are repeated alternately several times to remove the protective film of PMMA.
Finally, by drying the support and the graphene, the graphene can be transferred to the support.
In such a conventional transfer step, a chemical or the like is consumed, time is consumed, and productivity is low.
In a step of forming a coating on a surface of a graphene layer, removing the coating therefrom, scooping up the graphene layer with a silicon substrate or the like, or removing the graphene layer therefrom, the extremely thin graphene may be broken.
Conventionally, in order to form water passage holes in a graphene, the graphene has been heated in the air or in a mixed gas of oxygen and an inert gas (nitrogen, argon, helium, or the like) at a high temperature of about 300 to 500° C. (Patent Literature 1).
However, in this method, a film resist supporting the graphene is broken due to heat. In addition, control of a reaction is difficult and sizes of the water passage holes opened in the graphene are not uniform due to hole-opening by a combustion reaction of a graphite. Therefore, this method is not suitable for a filter molded article requiring uniform water passage holes.
Furthermore, cinders of the support formed of a resin or the like generated during combustion may contaminate the graphene to lower performance of a filter molded article.
In addition to the graphene, anion selection filter using carbon nanotubes (Patent Literature 4) or carbon nanohorns (Patent Literature 5) has been used (hereinafter, a single walled carbon nanohorn is abbreviated as SWNH).
As another method for forming a water passage hole in carbon nanomaterials, there is a method for attaching nitrates to carbon nanomaterials as an oxygen supply means and heating the carbon nanomaterials in vacuum or an inert gas at 300° C. to form holes (Patent Literature 6).